Tachometer nonfunctional on an 85 300D
 

My tach simply doesnt work. I have searched around and haven't found much information on fixing this. If we can get a list of things to check for any ways to troubleshoot perhaps we can make an informative tachometer troubleshooting thread as well as helping me get mine working!

Is your car a CA model?

in 85 ca and fed were identical... so it does not matter.

Here are a few threads to read:

This one has a lot of information on both CA and Fed cars:

1985 300D CA Emissions Tachometer repair

This is a thread on my troubleshooting my 1984 tach problems:

Figured out why my Tach won't work...

They are far from identical. The CA has a trap oxidizer and different emissions components including an emissions computer. I used to own one and even have a specific supplement shop manual for the car.

Two things to check......
OVP (overvoltage protection relay), right knee bolster panel under glove box, known to fail after many years. Easy to replace, always keep a spare in glove box.

Tach pickup on bell housing above flexplate. It's magnetic, clean it up.

Alan

Little known fuse hidden behind glove box could be blown.

I'm pretty sure he is only talking about the tach set up.....;)

My '85 tach has sat on 0 since I've owned the car. I've replaced the EGR computer, tach pickup, OVP relay. I doubt it's the gauge but I will swap that sometime when I'm around somebody with one.
Good luck with all that......

can someone post a pic of the overvoltage protection relay on a w123 and its exact location please.

Did you see this thread ?
http://www.peachparts.com/shopforum/diesel-discussion/138818-1985-300-d-tach-problem.html